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The recent observations of the positron fraction in cosmic rays by PAMELAindicate that the fraction of positrons to the total electronic component incosmic rays initially decreases in the energy region 1-10 GeV and increasesthereafter. In this paper, we show that it is natural to expect such anincrease of the positron fraction within the context of cosmic ray propagationmodels. It is shown that this ratio should reach an asymptotic value of ~0.6 atvery high energies. The specific measurements by PAMELA help us to distinguishamongst various models for cosmic ray propagation, and in particular, theysupport the nested leaky box model. They also provide, in conjunction with theobservations of the total electronic component by HESS, FERMI, ATIC, and otherexperiments, a way of estimating the spectrum of electrons directly acceleratedby discrete sources of cosmic rays in the Galaxy.

On the Positron Fraction and the Spectrum of the Electronic Component in Cosmic Rays